Methods related to junction ferrite devices having improved insertion loss performance

ABSTRACT

Disclosed are methods related to junction ferrite devices having improved insertion loss performance. In some implementations, a method of fabricating a circulator includes providing a grounding plane having a first side and a second side, positioning a magnet on the first side of the grounding plane, and positioning a ferrite-based disk on the second side of the grounding plane, the ferrite-based disk including a metalized layer on a grounding surface such that the metalized layer is in electrical contact with the second side of the grounding plane. In some implementations, a method for fabricating a ferrite disk assembly for a radio-frequency circulator includes forming a ferrite-based disk that includes a ferrite center portion, and forming a metalized layer on a first surface of the disk to improve electrical contact between the first surface of the disk with an external contact surface. Optionally, the metalized layer can be a silver layer formed on the grounding surface of the disk and having a desired thickness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Non-provisionalapplication Ser. No. 13/896,021, filed May 16, 2013, which claimspriority to U.S. Provisional Application No. 61/648,880 filed May 18,2012 and entitled “APPARATUS AND METHODS RELATED TO JUNCTION FERRITEDEVICES HAVING IMPROVED INSERTION LOSS PERFORMANCE,” the entirety ofboth of which is expressly incorporated by reference herein and shouldbe considered a part of this specification.

BACKGROUND Field

The present disclosure generally relates to methods related to junctionferrite devices having improved insertion loss performance inradio-frequency (RF) applications.

Description of the Related Art

In radio-frequency (RF) applications, junction ferrite devices such ascirculators can be utilized to, for example, selectively route RFsignals between an antenna, a transmitter, and a receiver. If an RFsignal is being routed between the transmitter and the antenna, thereceiver preferably should be isolated. Accordingly, a circulator issometimes also referred to as an isolator; and such an isolatingperformance can represent the performance of the circulator.

SUMMARY

In some implementations, the present disclosure relates to a circulatorthat includes a grounding plane having a first and a second side. Thecirculator further includes a magnet disposed on the first side of thegrounding plane. The circulator further includes a ferrite-based diskdisposed on the second side of the grounding plane. The ferrite-baseddisk includes a metalized layer on a grounding surface such that themetalized layer is in electrical contact with the second side of thegrounding plane.

In some embodiments, the ferrite-based disk can have a circular shape.The ferrite-based disk can include a circular shaped ferrite disksurrounded by a dielectric ring. The ferrite disk and the dielectricring can be secured to each other substantially free of glue. Theferrite disk and the dielectric ring can be formed by co-firing anassembly that includes a pre-sintered ferrite rod and an un-sintereddielectric cylinder fit around the ferrite rod.

In some embodiments, the metalized layer can have a thickness that is atleast 0.5 times a skin depth for a selected frequency range. In someembodiments, the thickness can be at least 1.0 times the skin depth. Insome embodiments, the thickness can be at least 2.0 times the skindepth.

In some embodiments, the grounding surface can have a finish so that anaverage value of feature sizes on the grounding surface is less than orequal to approximately 1.0 micron. In some embodiments, the averagevalue of feature sizes on the grounding surface can be less than orequal to approximately 0.5 micron. In some embodiments, the averagevalue of feature sizes on the grounding surface can be less than orequal to approximately 0.2 micron.

In some embodiments, the metalized layer can include a silver layer. Insome embodiments, the circulator can further include a center conductordisposed on the side opposite from the grounding side of theferrite-based disk. The circulator can further include a secondferrite-based disk, a second magnet, and a second grounding planeconfigured substantially similar to and arranged as mirror images of theferrite-based disk, the magnet, and the grounding plane about the centerconductor.

In accordance with a number of implementations, the present disclosurerelates to a method for fabricating a circulator. The method includesproviding a grounding plane having a first side and a second side. Themethod further includes positioning a magnet on the first side of thegrounding plane. The method further includes positioning a ferrite-baseddisk on the second side of the grounding plane. The ferrite-based diskincludes a metalized layer on a grounding surface such that themetalized layer is in electrical contact with the second side of thegrounding plane.

According to some implementations, the present disclosure relates to aferrite disk assembly for a radio-frequency (RF) circulator. The diskassembly includes a ferrite-based disk that includes a ferrite centerportion. The disk assembly further includes a metalized layer formed ona first surface of the disk to improve electrical contact between thefirst surface of the disk with an external contact surface.

In some embodiments, the first surface of the disk can include agrounding surface, such that the metalized layer improves the electricalcontact between the grounding surface of the disk and an externalgrounding surface. In some embodiments, the ferrite-based disk canfurther include a dielectric portion disposed around the periphery ofthe ferrite center portion. The ferrite center portion can have acircular shape, and the dielectric portion can have a circular ringshape.

In a number of implementations, the present disclosure relates to amethod for fabricating a ferrite disk assembly for a radio-frequency(RF) circulator. The method includes forming a ferrite-based disk thatincludes a ferrite center portion. The method further includes forming ametalized layer on a first surface of the disk to improve electricalcontact between the first surface of the disk with an external contactsurface.

In some implementations, the method can further include forming adesired finish surface on the first surface of the disk prior to themetalized layer formation. The forming of the metalized layer caninclude depositing a film of metal using an ink deposition method. Themethod can further include curing the deposited film of metal.

According to some teachings, the present disclosure relates to a methodfor improving insertion loss performance of a radio-frequency (RF)circulator. The method includes forming a ferrite-based disk thatincludes a ferrite center portion. The method further includes forming adesired finish for a grounding surface on the disk. The finish isselected to improve an electrical connection between the groundingsurface and one or more metal structures.

The desired finish includes an average feature size on the groundingsurface that is less than an average size resulting from a cut thatyields the ferrite-based disk.

In some implementations, the one or more metal structures can include ametalized layer formed on the grounding surface.

In accordance with some implementations, the present disclosure relatesto a packaged circulator module. The module includes a mounting platformconfigured to receive one or more components thereon. The module furtherincludes a circulator device mounted on the mounting platform. Thecirculator device includes a grounding plane having first and secondsides, and a magnet disposed on the first side of the grounding plane.The circulator device further includes a ferrite-based disk disposed onthe second side of the grounding plane. The ferrite-based disk has ametalized layer on a grounding surface such that the metalized layer isin electrical contact with the second side of the grounding plane. Themodule further includes a housing mounted on the mounting platform anddimensioned to substantially enclose and protect the circulator device.

In a number of implementations, the present disclosure relates to aradio-frequency (RF) circuit board. The circuit board includes a circuitsubstrate configured to receive a plurality of components. The circuitboard further includes a plurality of circuits disposed on the circuitsubstrate and configured to process RF signals. The circuit boardfurther includes a circulator device disposed on the circuit substrateand interconnected with at least some of the circuits. The circulatordevice includes a grounding plane having first and second sides, and amagnet disposed on the first side of the grounding plane. The circulatordevice further includes a ferrite-based disk disposed on the second sideof the grounding plane. The ferrite-based disk has a metalized layer ona grounding surface such that the metalized layer is in electricalcontact with the second side of the grounding plane. The circuit boardfurther includes a plurality of connection features configured tofacilitate passing of the RF signals to and from the RF circuit board.

In some implementations, the present disclosure relates to aradio-frequency (RF) system. The system includes an antenna assemblyconfigured to facilitate transmission and reception of RF signals. Thesystem further includes a transceiver in communication with the antennaassembly and configured to generate a transmit signal for transmissionby the antenna assembly and process a received signal from the antennaassembly. The system further includes a front end module configured tofacilitate routing of the transmit signal and the received signal. Thefront end module includes one or more circulators, with each circulatorincluding a grounding plane having first and second sides, and a magnetdisposed on the first side of the grounding plane. The circulatorfurther includes a ferrite-based disk disposed on the second side of thegrounding plane. The ferrite-based disk has a metalized layer on agrounding surface such that the metalized layer is in electrical contactwith the second side of the grounding plane.

In some embodiments, the system can include a base station. The basestation can be a cellular base station.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically show examples of circulators such as a3-port circulator and a 4-port circulator.

FIGS. 2A and 2B show examples of how magnetic fields can be applied toroute electromagnetic energy between selected ports while isolating anon-selected port of a circulator.

FIG. 3 shows an example configuration of a circulator device having apair of ferrite disks disposed between a pair of cylindrical magnets.

FIG. 4 shows an un-assembled view of a portion of the example circulatordevice of FIG. 3.

FIG. 5 shows that in some implementations, a ferrite disk or aferrite/dielectric disk assembly can include a metalized layer formed ona side of the disk that is grounded.

FIG. 6 shows an example of a disk assembly having a ferrite disk and adielectric ring that can be metalized to form the metalized disk of FIG.5.

FIG. 7 shows another example of a disk assembly having a ferrite diskand a dielectric ring that can be metalized to form the metalized diskof FIG. 5.

FIG. 8 shows a metalized disk that includes a metalized layer formed onthe grounding-side surface of a ferrite-based disk.

FIG. 9 shows an example configuration where a ferrite-based disk ismounted directly to a surface of a ground plane.

FIG. 10 shows an example configuration where a conductive metal foil ispositioned between a ferrite-based disk and a surface of a ground plane.

FIG. 11 shows an example configuration where a ferrite-based disk havinga metalized surface is mounted to a ground plane so that the metalizedsurface engages a surface of the ground plane.

FIG. 12 shows a comparison of insertion loss performance plots for thevarious configurations of FIGS. 9-11.

FIG. 13 shows an example of how surface finish of a ferrite-based devicecan affect insertion loss performance.

FIG. 14 shows a process that can be implemented to fabricate a metalizedferrite-based assembly having one or more features described herein.

FIG. 15 shows a process that can be implemented as a more specificexample of the metal layer formation step of FIG. 14.

FIG. 16 shows a process that can be implemented to manufacture a devicesuch as a circulator that includes a ferrite/dielectric disk having oneor more features described herein.

FIG. 17 shows an example packaged device having a circulator devicemounted on a packaging platform and enclosed by a housing structure.

FIG. 18 shows that in some embodiments, a packaged module such as theexample of FIG. 17 can be implemented in a circuit board or a module.

FIG. 19 shows that in some embodiments, the example circuit board ifFIG. 18 can be implemented in a front-end module of an RF apparatus.

FIG. 20 depicts an example wireless base-station having one or moreantennas that can be coupled to circuits and devices having one or morecirculators/isolators as described herein.

FIG. 21 shows a process that can be implemented to fabricate compositedisk assemblies.

FIG. 22 shows a process that can be implemented to fabricate compositedisk assemblies utilizing a co-firing technique.

FIG. 23 shows an example cylinder that can be formed from a dielectricceramic material.

FIG. 24 shows an example ferrite rod that can be dimensioned to fitwithin the cylinder of FIG. 23 for co-firing.

FIG. 25 shows a stage where a pre-fired ferrite rod is inserted into anunfired cylinder to form a rod-and-cylinder assembly for co-firing.

FIG. 26 shows the ferrite rod and the dielectric cylinder securedtogether by the co-firing process.

FIG. 27 shows that the co-fired rod-and-cylinder assembly can be slicedinto a plurality of composite magnetic-dielectric disk assemblies.

FIG. 28 shows a table with example compositional range of exampledielectric ceramic compositions that can be utilized for the dielectriccylinder of FIG. 23.

FIG. 29 shows a table with example electrical properties and examplesintering temperatures of example dielectric ceramic compositionsdescribed herein.

FIG. 30 shows a process that can be implemented for forming a dielectricceramic composition having one or more features as described herein.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

In some implementations, junction ferrite devices such as circulatorsare passive devices utilized in radio-frequency (RF) applications to,for example, selectively route RF signals between an antenna, atransmitter, and a receiver. If a signal is being routed between thetransmitter and the antenna, the receiver preferably should be isolated.Accordingly, a circulator is sometimes also referred to as an isolator;and such an isolating performance can represent the performance of thecirculator.

In some embodiments, a circulator can be a passive device having threeor more ports (e.g., ports for antenna, transmitter and receiver). FIGS.1A and 1B schematically show an example of a 3-port circulator 100 and a4-port circulator 104. In the example 3-port circulator 100, a signal isshown to be routed (arrow 102) from port 1 to port 2; and port 3 can besubstantially isolated from such a signal. In the example 4-portcirculator 104, a signal is shown to be routed (arrow 106) from port 1to port 2; and another signal is shown to be routed (arrow 108) fromport 3 to port 4. The two junctions of the signal paths in the exampleof FIG. 1B can be substantially isolated from each other. Otherconfigurations of 3 and 4-port circulators, as well as circulatorshaving other numbers of ports, can also be implemented.

In some implementations, a circulator can be based on ferrite materials.Ferrites are magnetic materials having very high ohmic resistance.Accordingly, ferrites have little or no eddy current when subjected tochanging magnetic fields, and are therefore suitable for RFapplications.

Ferrites can include Weiss domains, where each domain has a net non-zeromagnetization. When there is no external magnetic field influencing aferrite object, the Weiss domains are oriented substantially randomly,so that the ferrite as a whole has a net magnetization of approximatelyzero.

If an external magnetic field of sufficient strength is applied to theferrite object, the Weiss domains tend to align along the direction ofthe external magnetic field. Such a net magnetization can influence howan electromagnetic wave propagates within the ferrite object.

For example, and as depicted in FIGS. 2A and 2B, suppose that a circulardisk shaped ferrite object 110 is subjected to a substantially staticexternal magnetic field directed along the axis (perpendicular to theplane of paper) of the disk. In the absence of such an external field(not shown), an RF signal input into Port 1 and propagatingperpendicular to the disk axis splits into two rotating waves with asubstantially same propagation speed. One wave rotates clockwise aroundthe disk, and the other counter-clockwise around the disk, so as toyield a standing wave pattern. If Ports 2 and 3 are positioned equallyspaced azimuthally relative to Port 1 (about 120 degrees from eachother), the standing wave pattern results in approximately half of theincoming wave leaving each of Ports 2 and 3.

In the presence of such an external magnetic field, the propagationspeeds of the two rotating waves are no longer the same. Because of thedifference in the propagation speeds, the resulting standing wavepattern can yield a situation where substantially all of the energy ofthe incoming wave is passed to one of the two ports while the other portis substantially isolated.

For example, FIG. 2A shows a configuration where the axial staticmagnetic field (not shown) yielding a rotated standing wave patternrelative to the incoming wave propagation direction (along Port 1).Examples of electric field lines corresponding to such a standing wavepattern are depicted as 112 (along a plane of the disk) and 114, 116(along the axis of the disk). The example rotated standing wave patternresults in a substantial null in electric field strength at Port 3,thereby yielding substantial isolation of Port 3. On the other hand,Port 2 is depicted as having a similar (inverted) wave pattern as thatof the input at Port 1, and therefore transmits energy from Port 1 toPort 2.

FIG. 2B shows another example where an axial static magnetic field (notshown) yields a rotated standing wave pattern, such that a wave inputthrough Port 1 is passed to Port 3 as an output, and Port 2 issubstantially isolated. In some implementations, the two rotatedstanding wave patterns can be achieved by providing magnetic fields thatare higher and lower than a field value that results in a resonance inthe precession of ferrite domains.

FIG. 3 shows an example configuration of a circulator device 200 havinga pair of ferrite disks 202, 212 disposed between a pair of cylindricalmagnets 206, 216. FIG. 4 shows an un-assembled view of a portion of theexample circulator device 200.

In the example shown, the first ferrite disk 202 is shown to be mountedto an underside of a first ground plane 204. An upper side of the firstground plane 204 is shown to define a recess dimensioned to receive andhold the first magnet 206. Similarly, the second ferrite disk 212 isshown to be mounted to an upper side of a second ground plane 214; andan underside of the second ground plane 214 is shown to define a recessdimensioned to receive and hold the second magnet 216.

The magnets 206, 216 arranged in the foregoing manner can yieldgenerally axial field lines through the ferrite disks 202, 212. Themagnetic field flux that passes through the ferrite disks 202, 212 cancomplete its circuit through return paths provided by 220, 218, 208 and210 so as to strengthen the field applied to the ferrite disks 202, 212.In some embodiments, the return path portions 220 and 210 can be diskshaving a diameter larger than that of the magnets 216, 206; and thereturn path portions 218 and 208 can be hollow cylinders having an innerdiameter that generally matches the diameter of the return path disks220, 210. The foregoing parts of the return path can be formed as asingle piece or be an assembly of a plurality of pieces.

The example circulator device 200 can further include an inner fluxconductor (also referred to herein as a center conductor) 222 disposedbetween the two ferrite disks 202, 212. Such an inner conductor can beconfigured to function as a resonator and matching networks to the ports(not shown).

In some implementations, the example circulator device 200 can furtherinclude a high relative dielectric (Er) material disposed between theedge portion of the ferrite disks 202, 212 and the return path portions208, 218. Such a high Er dielectric can be formed as a ring dimensionedto fit between the corresponding ferrite disk and the outer return pathportion.

In some implementations, such a dielectric ring can be part of acomposite ferrite/dielectric TM resonator, where the dielectric replacessome of the ferrite. A high dielectric constant material can be used tokeep the diameter of the composite approximately the same as aferrite-only resonator at a desired frequency. In some embodiments, sucha dielectric material can have a dielectric constant value between about16 and 30, but are not necessarily confined to that range. In someimplementations, such a dielectric can provide a non-magnetic gapbetween the ferrite and the return path magnetic field to therebyimprove intermodulation distortion (IMD) reduction performance over aconfiguration where the ferrite extends further out to the return path.

FIG. 5 shows that in some implementations, a ferrite disk or aferrite/dielectric disk assembly 250 can include a metalized layer 260formed on a side of the disk 250 that is grounded. As described herein,such a metalized layer on the grounding side of the disk 250 can yieldsignificant improvements in insertion loss performance when compared toa bare disk configuration or a configuration where a highly conductivemetal foil is disposed between a ferrite-based disk and the groundplane. Additional details concerning such a metalized layer 260 aredescribed herein in greater detail. In some embodiments, the disk 250having the metalized layer 260 can be utilized as the ferrite baseddisks 202, 212 described in reference to FIGS. 3 and 4.

For the purpose of description, a disk can include a ferrite-only disk,or a ferrite-disk and a dielectric ring assembly. In the example shownin FIG. 5, the disk 250 having the metalized layer 260 includes aferrite disk 252 and a dielectric ring 254. It will be understood thatone or more features of the present disclosure can also be implementedin a configuration where a disk is a ferrite-only disk. It will also beunderstood that one or more features of the present disclosure can alsoapply to other shaped disks or plates. For example, a triangle-shapeddisk can include a metalized side and provide advantages associated withsuch metallization.

In some implementations, the foregoing metallization of ferrite-baseddisks can improve insertion loss performance of the circulator. Theinsertion loss of a ferrite device can include a contribution from theground plane both in terms of conductivity and conductor path length. Inaddition, air gaps can exist in configurations where a conductive metalfoil is used between a ferrite-based disk and the ground plane. Such airgaps can introduce spurious responses which can appear as small peaks inthe insertion loss response, and/or reduce the symmetry in thecirculator operation resulting in poorer return loss and isolation. Suchundesirable effects associated with air gaps can result in a lower yieldof good production circulator devices.

As described herein, the use of a metalized layer formed on a surface ofa disk can improve insertion loss performance. In some embodiments, sucha metalized layer can include a thick film metallization layer formedfrom, for example, silver or copper. Such an improvement in insertionloss performance can be due to, for example, elimination of air gaps andimproved conductivity provided by the thick film metallization layer. Insome embodiments, the use of a polished ferrite/dielectric assembly onthe side in contact with the metal forming the ground plane can reducethe effective conductor length. Embodiments using a gluedferrite/dielectric assembly typically have significant additionaldielectric loss from the glue; thus, eliminating the glue can improvedevice insertion loss performance. Examples of the foregoing featuresare described herein in greater detail.

FIG. 6 shows that in some implementations, a disk assembly 202 having aferrite disk 232 and a dielectric ring 234 can be metalized to form themetalized disk 250 of FIG. 5. In the example of FIG. 6, the ferrite disk232 and the dielectric ring 234 can be secured together by an adhesive238. A surface 236 that will be engaging the ground plane (not shown)can be metalized.

FIG. 7 shows that in some implementations, a disk assembly 202 having aferrite disk 242 and a dielectric ring 244 can be metalized to form themetalized disk 250 of FIG. 5. In the example of FIG. 7, the ferrite disk242 and the dielectric ring 244 can be secured together by a co-firingtechnique. Additional details concerning examples of dielectricmaterials suitable for such a dielectric ring and the co-firingtechnique are described herein. Such a co-firing technique can yield asecure adhesive-free joint 248 between the ferrite disk 242 and thedielectric ring 244. A surface 246 that will be engaging the groundplane (not shown) can be metalized as described herein.

In some implementations, the foregoing co-fired configuration can beparticularly useful when temperatures associated with metallizationtechniques exceed temperatures associated with the glued configurationof FIG. 6. For example, some glues that can be utilized to form thejoint 238 may be organic and therefore not be able to withstandtemperatures in excess of a few hundred degrees C. Using a co-firedassembly, where there is no glue, the assembly can withstandtemperatures in excess of 1000° C. Accordingly, it is possible to usemetallization techniques such as thick film ink deposition, which usetemperatures of less than 1000° C., on co-fired assemblies.

FIG. 8 shows a metalized disk 250 that includes a metalized layer 260formed on the grounding-side surface 256 of a ferrite-based disk 202(e.g., a ferrite disk 252 surrounded by a dielectric ring 254). As shownin an enlarged view 262, the metalized layer 260 can have a thickness of“t.” Examples of such a thickness are described herein in greaterdetail. In some implementations, metallization techniques such as thickfilm ink deposition can be utilized to form the metalized layer 260.Other known metallization techniques can also be utilized to form themetalized layer 260.

FIGS. 9-11 show various configurations of circulators 200 whereferrite-based disks are coupled to a ground plane 204 in differentmanners. FIG. 9 shows a configuration 270 where a ferrite-based disk(230 of FIG. 6 or 240 of FIG. 7) is mounted directly to a surface 272 ofthe ground plane 204. FIG. 10 shows a configuration 280 where aconductive metal foil 282 is positioned between a ferrite-based disk(230 of FIG. 6 or 240 of FIG. 7) and a surface 272 of the ground plane204. FIG. 11 shows a configuration 290 where a ferrite-based disk (250of FIG. 8) having a metalized surface 260 is mounted to the ground plane204 so that the metalized surface 260 engages a surface 272 of theground plane 204.

FIG. 12 shows a comparison of insertion loss performance plots forvarious configurations that can be grouped into one of the threeconfigurations of FIGS. 9-11. Table 1 lists measurements correspondingto the various configurations.

TABLE 1 General Trace Insertion configuration Trace marker Frequencyloss FIG. 9 Co-fire/Slice to size 1 1.805 GHz −0.133 dB FIG. 9Co-fire/Slice to size 2 1.880 GHz −0.123 dB FIG. 10 Co-fire/Slice to 31.805 GHz −0.113 dB size + foil FIG. 10 Co-fire/Slice to 4 1.880 GHz−0.119 dB size + foil FIG. 11 Co-fire/Slice to 5 1.805 GHz −0.113 dBsize + thin film FIG. 11 Co-fire/Slice to 6 1.880 GHz −0.113 dB size +thin film FIG. 11 Co-fire/Slice to 7 1.805 GHz −0.106 dB size + thickfilm FIG. 11 Co-fire/Slice to 8 1.880 GHz −0.102 dB size + thick filmFIG. 9 Standard process 9 1.805 GHz −0.155 dB FIG. 9 Standard process 101.880 GHz −0.161 dB FIG. 10 Standard process + foil 11 1.805 GHz −0.137dB FIG. 10 Standard process + foil 12 1.880 GHz −0.136 dB FIG. 11Co-fire/Lap (32 13 1.805 GHz −0.112 dB finish) + thick film FIG. 11Co-fire/Lap (32 14 1.880 GHz −0.119 dB finish) + thick film FIG. 11Co-fire/Lap (12 15 1.805 GHz −0.107 dB finish) + thick film FIG. 11Co-fire/Lap (12 16 1.880 GHz −0.109 dB finish) + thick film FIG. 11Co-fire/Lap (Polish) + 17 1.805 GHz −0.090 dB thick film FIG. 11Co-fire/Lap (Polish) + 18 1.880 GHz −0.092 dB thick film

In FIG. 12 and Table 1, “Co-fire” indicates a co-fired assembly offerrite disk and dielectric ring as described herein in reference toFIG. 7, and “Standard” indicates a glued assembly of ferrite disk anddielectric ring as described herein in reference to FIG. 6. “Slice tosize” indicates an as-sliced finish in a range of 20 to 40 micro-inches(0.5 to 1.0 micron). “Lap (32 finish)” indicates a lapped surface finishthat is less than 32 micro-inches (less than 0.8 micron). “Lap (12finish)” indicates a lapped surface finish that is less than 12micro-inches (less than 0.3 micron). “Lap (Polish)” indicates a polishedsurface finish that is less than 4 micro-inches (less than 0.1 micron).“Thin film” indicates a metalized layer of silver with a thickness ofabout one skin depth; and “thick film” indicates a metalized layer ofsilver with a thickness of about two skin depths.

The standard process used for comparison was a glued, outside diametersawn and surface ground (32 micro-inch) assembly in the ferrite deviceat 1.805 and 1.880 GHz (markers 9 and 10). This was then compared with astandard process assembly with metal foil as the ground plane (markers11 and 12). These results were then compared with the co-fired andsliced to size assemblies (as-sliced finish) with (markers 3 and 4) andwithout foil (markers 1 and 2). These results showed that theimprovement due to co-firing was approximately 0.02 dB, and theimprovement due to foil versus no foil was also about 0.02 dB.

To test the effect of microwave skin depth, which is approximately 4microns for metalized layers of aluminum, gold or silver at 2GHz, theeffect of using x1 and x2 skin depths of silver metalized film wasmeasured. The results show that thin film metallization of aboutone-skin depth (markers 5 and 6) was slightly more effective than foil(markers 3 and 4). The two-skin depths configuration (markers 7 and 8)provided an improvement of approximately 0.01 dB over the foilconfiguration (markers 3 and 4).

Using the two-skin depth thickness of thick film silver, the insertionloss then was progressively reduced from a lapped 32 micro-inch (markers13 and 14) to an as-sliced finish (markers 7 and 8), to a lapped 12micro-inch (markers 15 and 16) and finally a polished 4 micro-inchfinish (markers 17 and 18). The example effect of surface finish of theassembly on the ground plane side, with thick film silver ofapproximately twice the skin depth, is shown in FIG. 13.

The foregoing example results indicate that significant improvements ininsertion loss performance can be obtained with co-fired assemblies overglued assemblies. Improvements in insertion loss performance can also beobtained with a metalized film formed on the grounding surface of aferrite-based assembly. An increased thickness of such a metalized filmcan provide significant improvements in insertion loss performance. Insome embodiments, a metalized film having a thickness “t” can be formedon the grounding surface of a ferrite-based assembly, and such athickness can be based on skin depth associated with a range or value offrequency and a metal being used (e.g., aluminum, gold, copper, tin,nickel, silver, or alloy of these metals). In some embodiments, themetalized film thickness “t” can be at least 0.5 times the skin depth,at least 1.0 times the skin depth, at least 1.5 times the skin depth, orat least 2.0 times the skin depth.

As shown in FIG. 13, significant improvements in insertion lossperformance can be obtained by providing finer surface finishes on theside of the ferrite-based assembly that is metalized. In someembodiments, a surface finish can be provided on a ferrite basedassembly as described herein so that an average value of feature sizeson the surface is less than or equal to approximately 1.0 micron, 0.8micron, 0.6 micron, 0.5 micron, 0.4 micron, 0.3 micron, 0.2 micron, or0.1 micron.

FIGS. 14-16 show example processes that can be implemented to fabricatea metalized ferrite-based assembly and a circulator/isolator using suchan assembly. FIG. 14 shows a process 300 that can be utilized tofabricate a metalized ferrite-based assembly. A ferrite rod can befabricated based on blocks 302 to 308, and a dielectric cylinder can befabricated based on blocks 310 and 312. When assembled and cut intodisks, the ferrite rod yields a ferrite disk (e.g., 252 in FIG. 8), andthe dielectric cylinder yields a dielectric ring (e.g., 254).

In block 302, powder for forming the ferrite rod can be prepared. Insome implementations, such a powder can be by mixing selected rawmaterials to yield a dry granulated mixture. The granulated mixture canbe pre-sintered to yield a pre-sintered material. The pre-sinteredmaterial can be milled to yield reduced particle size of thepre-sintered material. Such a milling process can yield refined andregulated particles from the pre-sintered material. The milled materialcan be dried by, for example, a spray-drying process. Such aspray-drying process can be used to produce free-flowing powder suitablefor forming by, for example, pressing. The spray-dried powder materialcan be separated into one or more groups of particle-size ranges toyield one or more powders having desired ranges of particle sizes.

In block 304, a rod can be formed from the powder. In someimplementations, such a rod can be formed by techniques such aspress-forming or extrusion.

In block 306, the formed rod can be pre-sintered to yield a reducedlateral dimension such as diameter. In block 308, a desired lateraldimension (e.g., diameter) can be obtained by, for example, machining ofthe rod.

To fabricate the dielectric cylinder, powder with desired contents canbe prepared in block 310. In some implementations, such powderpreparation can be similar to that described in reference to block 302.In block 312, a hollow cylinder can be formed from the prepared powder.In some implementations, such a cylinder can be formed by techniquessuch as press-forming or extrusion.

In block 320, the pre-sintered rod and the un-sintered cylinder can beassembled. As described herein, such a configuration allows the cylinderto fit over the rod, and upon co-firing of the assembly (block 322), thecylinder can shrink around the pre-shrunk rod to thereby yield aglue-less and robust joint.

In block 324, one or more disks can be formed (e.g., cut) from theco-fired rod-and-cylinder assembly. In block 326, a desired finishsurface can be formed on a grounding side of a cut disk. In block 328, ametal layer can be formed on the finished surface.

FIG. 15 shows a process 340 that can be implemented as a more specificexample of block 328 of FIG. 14. In block 342, a co-firedferrite/dielectric disk assembly can be obtained. In block 344, asurface having a desired smoothness can be formed on a grounding side ofthe ferrite/dielectric disk assembly. In block 346, a metal layer havinga desired thickness can be deposited on the smoothed surface. In block348, the deposited metal layer can be cured.

FIG. 16 shows a process 350 that can be implemented to assemble, forexample, a circulator device of FIG. 3 based on a ferrite/dielectricdisk having one or more features described herein. In block 352, aferrite/dielectric disk assembly having a metalized grounding surfacecan be obtained. In block 354, the disk assembly can be positionedrelative to a grounding plate so that the metalized surface of the diskassembly is in contact with a surface on one side of the groundingplate. In block 356, a magnet can be mounted on the other side of thegrounding plate to form a sub-assembly. In block 358, two of suchsub-assemblies can be positioned in an approximate mirror imageorientation about a center conductor plate to yield a circulator device.

In some embodiments, a circulator device fabricated in the foregoingmanner and having one or more features as described herein can beimplemented as a packaged modular device. FIG. 17 shows an examplepackaged device 400 having a circulator device 200 mounted on apackaging platform 404 and enclosed by a housing structure 402. Theexample platform 404 is depicted as including a plurality of holesdimensioned to allow mounting of the packaged device 400. The examplepackaged device 400 is shown further include example terminals 406 a-406c configured to facilitate electrical connections to, for example, thethree circulator/isolator ports described herein in reference to FIGS. 1and 2.

FIG. 18 shows that in some embodiments, a packaged module 400 such asthe example of FIG. 17 can be implemented in a circuit board or module410. Such a circuit board can include a plurality of circuits configuredto perform one or more radio-frequency (RF) related operations. Thecircuit board 410 can also include a number of connection featuresconfigured to allow transfer of RF signals and power between the circuitboard 410 and components external to the circuit board 410.

In some embodiments, the example circuit board 410 can include RFcircuits associated with a front-end module of an RF apparatus. As shownin FIG. 19, such an RF apparatus can include an antenna 412 that isconfigured to facilitate transmission and/or reception of RF signals.Such signals can be generated by and/or processed by a transceiver 414.For transmission, the transceiver 414 can generate a transmit signalthat is amplified by a power amplifier (PA) and filtered (Tx Filter) fortransmission by the antenna 412. For reception, a signal received fromthe antenna 412 can be filtered (Rx Filter) and amplified by a low-noiseamplifier (LNA) before being passed on to the transceiver 414. In theexample context of such Tx and Rx paths, circulators and/or isolators400 having one or more features as described herein can be implementedat or in connection with, for example, the PA circuit and the LNAcircuit.

In some embodiments, circuits and devices having one or more features asdescribed herein can be implemented in RF applications such as awireless base-station. FIG. 20 depicts an example wireless base-station450 having one or more antennas 412 configured to facilitatetransmission and/or reception of RF signals. Such antenna(s) can becoupled to circuits and devices having one or more circulators/isolatorsas described herein.

As described herein, some circulator/isolators can be based on compositedisk assemblies, with each having a ferrite rod within a dielectriccylinder. Some of such disk assemblies can be formed utilizing aco-firing technique. Examples related to such a co-firing technique aredescribed in reference to FIGS. 21-27. Examples of compositions andmethods that can be implemented to form dielectric materials (e.g., forthe dielectric cylinder) are also described in reference to FIGS. 28-30.

Examples Related to Co-Firing of Magnetic and Dielectric Materials

A method for making a composite magnetic-dielectric disc assembly caninclude forming a dielectric ceramic cylinder, forming a magneticceramic rod, assembling the magnetic ceramic rod coaxially inside thedielectric ceramic cylinder to form a rod-and-cylinder assembly, kilning(firing) the rod-and-cylinder assembly, slicing the rod-and-cylinderassembly to form a plurality of composite magnetic-dielectricdisc-shaped assemblies. The magnetic-dielectric disc assemblies can beused in manufacturing, for example, circulators, isolators or similarelectronic components. Accordingly, the method for making the discassemblies can be included as part of a method for making suchelectronic components.

Circulators and isolators can be configured as passive electronicdevices that are used in high-frequency (e.g., microwave) radiofrequency systems to permit a signal to pass in one direction whileproviding high isolation to reflected energy in the reverse direction.Circulators and isolators can commonly include a disc-shaped assemblyhaving a disc-shaped ferrite or other ferromagnetic ceramic element,disposed concentrically within an annular dielectric element. A commonlyused ferrite materials can include yttrium-iron-garnet (YIG), due to itslow-loss microwave characteristics. The annular dielectric element canbe made of ceramic material.

An example process for making the above-referenced composite discassemblies is illustrated by the flow diagram of FIG. 21. At step 12, acylinder can be formed from a dielectric ceramic material. At step 14,the (unfired or “green”) cylinder can be fired in a kiln (commonlyreferred to simply as “firing”). At step 16, the outside surface of thecylinder can be machined to ensure its outside diameter (OD) is of aselected dimension. Achieving precise dimensions in the assemblyelements can be important because the dimensions can affect microwavewaveguide characteristics. At step 18, the inside surface of thecylinder can be similarly machined to ensure its inside diameter (ID) isof a selected dimension. In addition, at step 20, a rod can be formedfrom a magnetic ceramic material. At step 22, the rod can be fired, andat step 24 its surface can be machined to a selected OD. The rod OD canbe slightly less than the cylinder OD so that the rod can be fittedsecurely within the cylinder, as described herein. Achieving a close fitthat promotes good adhesion between the rod and cylinder can be a reasonthat both the outside surface of the rod and the inside surface of thecylinder are machined to precise tolerances.

At step 26, epoxy adhesive can be applied to the one or both of the rodand cylinder. At step 28, the rod can be inserted inside the cylinder toform a rod-and-cylinder assembly, and the epoxy can be allowed to cure(harden), as indicated by step 30. At step 32, the outside surface ofthe rod-and-cylinder assembly can be machined to a precise OD. At step34, the rod-and-cylinder assembly can be sliced into a number of discassemblies. Each disc assembly thus can include a magnetic ceramic discdisposed concentrically within a dielectric ceramic ring. Each discassembly can have a thickness of, for example, several millimeters.

In some implementations, the time involved in machining the insidesurface of the cylinder to promote adhesion, applying epoxy to theparts, carefully handling and assembling the epoxy-laden parts, andcuring the epoxy, can contribute to inefficiency in the process.

In accordance with some implementations, a method for making a compositemagnetic-dielectric disc assembly can include forming a dielectricceramic cylinder, forming a magnetic ceramic rod, assembling themagnetic ceramic rod coaxially inside the dielectric ceramic cylinder toform a rod-and-cylinder assembly, firing the rod-and-cylinder assembly,slicing the rod-and-cylinder assembly to form a plurality of compositemagnetic-dielectric disc-shaped assemblies. The magnetic-dielectric discassemblies can be used in manufacturing, for example, circulators,isolators or similar electronic components. Accordingly, the method formaking disc assemblies can be included as part of a method for makingsuch electronic components.

In accordance with some implementations, a process for making compositemagnetic-dielectric disc assemblies is illustrated by the flow diagramof FIG. 22. Referring briefly to FIGS. 23-27, the process can involve adielectric ceramic cylinder 36 and a magnetic ceramic rod 38.

Returning to FIG. 22, at step 40, cylinder 36 (FIG. 23) can be formedfrom a dielectric ceramic material by, for example, any suitableconventional process known in the art for making such elements (e.g.,dielectric ceramic elements of the types used in high frequencyelectronic components). Similarly, at step 42, rod 38 (FIG. 24) can beformed from a magnetic ceramic material by, for example, any suitableconventional process. At step 44, rod 38 can be sintered by firing it ina kiln (not shown). Some examples of materials and firing temperaturesare set forth below, following this process flow description. However,it will be understood that other materials and processes can beutilized.

At step 46, the outside surface of rod 38 can be machined to ensure itis of an outside diameter (OD) that is less than the inside diameter(ID) of cylinder 36. At step 48, (the now pre-fired) rod 38 can bereceived in (the unfired or “green”) cylinder 36 to form therod-and-cylinder assembly shown in FIG. 25. Though FIG. 25 is notnecessarily to scale, it is noted that the OD of rod 38 can be slightlysmaller than the ID of cylinder 36 to enable rod 38 to be received incylinder 36.

At step 50, cylinder 36 and rod 38 can be co-fired. That is, therod-and-cylinder assembly (FIG. 25) can be fired. The co-firingtemperature is preferably lower than the temperature at which rod 38 wasfired at step 44, to ensure that the physical and electrical propertiesof rod 38 remain unchanged. The co-firing temperature can be within aknown range in which such cylinders are conventionally fired. In someembodiments, co-firing can cause cylinder 36 to shrink around rod 38,thereby securing them together, as shown in FIG. 26. At step 52, theoutside surface of the rod-and-cylinder assembly can be machined toensure it is of a specified or otherwise predetermined OD.

At step 54, the rod-and-cylinder assembly can be sliced into compositemagnetic-dielectric disc assemblies 56, shown in FIG. 27. Compositemagnetic-dielectric disc assemblies 56 can be used in manufacturing highfrequency electronic components. The example method described herein inreference to FIGS. 22-27 can be more economical than methods thatutilize adhesives.

In an example, rod 38 can be made of yttrium-iron-garnet fired at orabove about 1400 degrees C. Suitable material of this type iscommercially available from a number of sources, including, for example,Trans-Tech, Inc. (a subsidiary of Skyworks Solutions, Inc.) ofAdamstown, Md. Cylinder 36 can be made of a ceramic material having acomposition of MgO—CaO—ZnO—Al2O3-TiO2 co-fired with rod 38 at atemperature of about 1310 degrees C.

In another example, rod 38 can be made of calcium and vanadium-dopedyttrium-iron-garnet fired at a temperature at or above 1350 degrees C.Suitable material of this type is commercially available from a numberof sources, including Trans-Tech, Inc. (a subsidiary of SkyworksSolutions, Inc.) of Adamstown, Md. Cylinder 36 can be made of a ceramicmaterial having a composition of MgO—CaO—ZnO—Al2O3-TiO2 co-fired withrod 38 at a temperature of about 1310 degrees C.

Examples Related to Dielectric Ceramic Compositions

In some implementations, dielectric parts described herein (e.g.,dielectric ceramic cylinder 36 of FIGS. 23-27) can include a dielectricceramic composition having a main component group, where the maincomponent group can be represented by Mg_(x)Ca_(y)Zn_(z)TiO_(2+x+y+z),where the sum of x, y, and z is less than or equal to 1.0 such that thedielectric ceramic composition has a wider sintering temperature rangeand reduced exaggerated grain growth. In an example, x can be greaterthan 0.0 and less than 1.0, y can be greater than 0.0 and less than 1.0,and z can be greater than 0.0 and less than 1.0. The dielectric ceramiccomposition can further include between 0.0 and 50.0 percent by weightof aluminum oxide. The dielectric ceramic composition can furtherinclude copper oxide. The dielectric ceramic composition can furtherinclude boron oxide.

Dielectric ceramic compositions, such as dielectric ceramic compositionsthat include magnesium (Mg), calcium (Ca), and titanium (Ti), arecommonly used in devices such as dielectric filters, dielectricresonators, and dielectric couplers in various types of radio-frequency(RF) and microwave systems. However, a dielectric ceramic compositionthat includes Mg, Ca, and Ti, typically has a narrow sinteringtemperature range and exaggerated grain growth. Since the narrowsintering temperature range is more difficult to maintain in thesintering kiln, such dielectric ceramic may be under-fired (e.g.,sintered at a temperature below a desired temperature range) orover-fired (e.g., sintered at a temperature above the desiredtemperature range) in the sintering kiln. Under-firing and over-firingcan cause various problems in the resulting dielectric composition.

For example, under-firing can cause undesirable variations in thedielectric constant, low density, and reduced mechanical strength. Inanother example, over-firing can cause undesirable exaggerated graingrowth, which can also reduce the mechanical strength. Furthermore,under-firing or over-firing caused by a narrow sintering temperaturerange can result in low manufacturing yield.

In some implementations, a dielectric ceramic composition can have awide sintering temperature range and a reduced exaggerated grain growth.In some implementations, a dielectric ceramic composition can include amain component group, where the main component group is represented byMg_(x)Ca_(y)Zn_(z)TiO_(2+x+y+z), where the sum of x, y, and z is lessthan or equal to 1.0 such that the dielectric ceramic composition has awider sintering temperature range and reduced exaggerated grain growth.In some embodiments, x can be greater than 0.0 and less than 1.0, y canbe greater than 0.0 and less than 1.0, and z can be greater than 0.0 andless than 1.0.

In some embodiments, the dielectric ceramic composition can furtherinclude between 0.0 and 50.0 percent by weight of aluminum oxide. Thedielectric ceramic composition can further include copper oxide. Thedielectric ceramic composition can further include boron oxide.

In some embodiments, “x,” “y,” and “z” inMg_(x)Ca_(y)Zn_(z)TiO_(2+x+y+z) can determine the respective relativeratio of Mg (magnesium), Ca (calcium), and Zn (zinc). The ratio of “O”(oxygen) in the main component group can be determined by the sum2+x+y+z. In an example embodiment, “x” can be between 0.0 and 2.0, “y”can be greater than 0.0 and less than or equal to 1.0, “z” can bebetween 0.0 and 0.03, and “x+y+z” can be between 1.0 and 2.0. In anotherexample embodiment, “x” can be between 0.0 and 2.0, “y” can be greaterthan 0.0 and less than or equal to 1.0, “z” can be greater than 0.09 andless than or equal to 1.0, and “x+y+z” can be between 1.0 and 2.0.

In some embodiments, an amount of aluminum oxide (Al₂O₃) can be added tothe main component group (Mg_(x)Ca_(y)Zn_(z)TiO_(2+x+y+z)). By way of anexample, between 0.0 and 50.0 percent by weight of Al₂O₃ can be added tothe main component group. For the purpose of description, “percent byweight” can defined as the percentage of the weight of the maincomponent group of the dielectric ceramic composition that is added bythe additional component, such as Al₂O₃. For example, if the maincomponent group of the dielectric ceramic composition weighs 100.0kilograms, an addition of 50.0 percent by weight of Al₂O₃ would be equalto an amount of Al₂O₃ weighing 50.0 kilograms.

The addition of Al₂O₃ to the main component group can alter theprocessing parameters, such as the sintering temperature, and otherproperties of the dielectric ceramic composition. In other embodiments,between 0.0 and 8.0 percent by weight of boron oxide (B₂O₃) and/orbetween 0.0 and 8.0 percent by weight of copper oxide (CuO) can be addedto the main component group to reduce the sintering temperature (e.g.,the final firing temperature) of the dielectric ceramic composition.

FIG. 28 shows a table with example compositional range of exampledielectric ceramic compositions in accordance with respectiveembodiments described herein. Table 1100 shows a summation of thecompositional range of dielectric ceramic compositions according tovarious respective embodiments as described herein. Table 1100 includescolumns 1102, 1104, 1106, 1108, 1110, and rows 1112, 1114, and 1116. Intable 1100, column 1102 shows the range of “x,” column 1104 shows therange of “y,” column 1106 shows the range of “z,” column 1108 shows therange of “x+y+z,” and column 1110 shows the percent by weight of Al₂O₃that can be added to the main component group(Mg_(x)Ca_(y)Zn_(z)TiO_(2+x+y+z)). Rows 1112, 1114, and 1116 in table1100 show the ranges of “x,” “y,” “z,” and “x+y+z” and the percent byweight of Al₂O₃ in respective example embodiments of the dielectricceramic composition.

FIG. 29 shows a table with example electrical properties and examplesintering temperatures of example dielectric ceramic compositionsdescribed herein. Table 1200 includes columns 1202 a through 1202 i androws 1204 a through 1204 n. In table 1200, columns 1202 a, 1202 b, 1202c, and 1202 d show respective values of “x,” “y,” “z,” and “x+y+z” inthe main component group (Mg_(x)Ca_(y)Zn_(z)TiO_(2+x+y+z)). Column 1202e shows the percent by weight of Al₂O₃, CuO, or B₂O₃, column 1202 fshows the value of the dielectric constant (ε′), column 1202 g shows thevalue of the temperature coefficient of frequency (τf) in parts permillion per degree centigrade (PPM/° C.), column 1202 h shows the valueof the quality factor times frequency (Q×F) in gigahertz (GHz), andcolumn 1202 i shows the value of the sintering temperature in ° C. Intable 1200, rows 1204 a through 1204 n show the dielectric ceramiccomposition, electrical properties, and sintering temperature ofrespective example embodiments.

As shown in rows 1204 j, 1204 k, and 12041 of table 1200, for the samedielectric ceramic composition (e.g., for the same values of “x,” “y,”“z,” and “x+y+z” and the same percent by weight of Al₂O₃), a dielectricceramic composition can achieve a wide sintering temperature range of85.0° C. (e.g., between 1275.0° C. and 1360.0° C.). Additionally, adielectric ceramic composition can have a dielectric constant ofapproximately 20.0, a uniform density, and significantly reducedexaggerated grain growth. As a result, a dielectric ceramic compositioncan have an increased manufacturing yield. In contrast, other dielectricceramic compositions that include Mg, Ca, and Ti typically have a narrowsintering temperature range of approximately 5.0° C. to 10.0° C. As aresult of the narrow sintering temperature range, the such dielectricceramic compositions can have a varying dielectric constant, significantexaggerated grain growth, and non-uniform density, which can cause areduced manufacturing yield. Additionally, as shown in row 1204 n oftable 1200, with the addition of 1.0 percent by weight of B₂O₃, anembodiment of the dielectric ceramic composition can have a lowsintering temperature of 1000.0° C.

FIG. 30 shows a flowchart illustrating an example method for forming adielectric ceramic composition having one or more features as describedherein. Certain details and features have been left out of flowchart1300 that are apparent to a person of ordinary skill in the art.

At step 1302 of flowchart 1300, a batched powder can be formed includingcompounds of elements of a main component group represented byMg_(x)Ca_(y)Zn_(z)TiO_(2+x+y+z). The batched powder can include MgO,CaCO₃, ZnO, and TiO₂, which are compounds of respective elements Mg, Ca,Zn, and Ti of the main component group. The batched powder can be formedby appropriately weighing out MgO, CaCO₃, ZnO, and TiO₂ according toratios determined by selected values of “x,” “y,” and “z” as describedherein. In other embodiments, different compounds of the elements Mg,Ca, Zn, and Ti of the main component group may be used to form thebatched powder.

In some embodiments, the values “x,” “y,” and “z” can be greater than0.0 and less than 1.0 and the value of “x+y+z” can be less than or equalto one. In other embodiments, the value of “x” can be greater than 0.0and less than 2.0, the value of “y” can be greater than 0.0 and lessthan or equal to 1.0, the value of “z” can be greater than 0.0 and lessthan 0.03 or greater than 0.09 and less than or equal to 1.0, and thevalue of “x+y+z” can be greater than 1.0 and less than 2.0.

After the batched powder has been formed, between 0.0 and 50.0 percentby weight of Al₂O₃ can be added to the batched powder. In an example,between 0.0 and 50.0 percent by weight of Al₂O₃ can be added to thefabrication process at a subsequent process step. In other embodiments,between 0.0 and 8.0 percent by weight of B₂O₃ and/or between 0.0 and 8.0percent by weight of CuO can be added to the batched powder to reducethe sintering temperature.

At step 1304, an initial slurry can be formed and the initial slurry canbe wet mixed, milled, and dried. The initial slurry can be formed byadding an appropriate dispersing agent and deionized water to thebatched powder. The initial slurry can then be wet mixed, milled, anddried in an oven to form a mechanical mixture. The initial slurry can bemilled, for example, in a vibratory mill. However, other milling devicesmay also be used to mill the initial slurry. At step 1306, a calcineprocess can be utilized to form a homogenous powder. The homogenouspowder can be formed in the calcine process by heating the mechanicalmixture in an oven at an appropriate temperature for an appropriateduration so as to cause the individual components in the mechanicalmixture to chemically react and, thereby, fuse together. By way ofexample, the calcine process can be performed at a temperature ofapproximately 1150.0° C. for approximately 8.0 hours. However, thetemperature and duration of the calcine process can vary depending onthe particular dielectric ceramic composition that is being formed.

At step 1308, a final slurry can be formed and milled to achieve adesired particle size. The final slurry can be formed by mixing thehomogeneous powder formed at step 1306 with deionized water. The finalslurry can then be milled to achieve a desired particle size by using avibratory mill or other appropriate milling device. The milling processcan provide a medium particle size, for example, of approximately 2.5microns having a particle distribution such that approximately 50.0percent of the particles are smaller than 2.5 microns and approximately50.0 percent of the particles are larger than 2.5 microns. The mediumparticle size range can be, for example, between 2.4 microns and 2.7microns.

At step 1310, a binder can be added to the final slurry and the finalslurry can be spray dried to form flowable granulates. The binder canbe, for example, polyvinyl alcohol or methyl cellulose, depending onwhether a dry-pressing process or an extrusion process, respectively, isutilized to shape the flowable granulates in a subsequent process step.The final slurry can be spray dried to form the flowable granulates inan appropriate spray drying process. At step 312, the flowablegranulates can be forced into a desired shaped and a sintering processcan be performed to form a desired dielectric ceramic composition. Theflowable granulates can be formed into a desired shaped by utilizing adry-pressing process or an extrusion process, for example. In thesintering process, the shaped granulates can be heated to a sufficientlyhigh temperature to form a dielectric ceramic composition. By way ofexample, the sintering temperature range can be between 1275.0° C. and1360.0° C. Thus, the foregoing example can achieve a wide sinteringtemperature range of approximately 85.0° C.

In other embodiments, between 0.0 and 8.0 percent by weight of B₂O₃ orCuO can be utilized as an additive to achieve a significantly lowersintering temperature. By way of example, 1.0 percent by weight of B₂O₃can be added at step 1302 of the formation process to achieve asintering temperature of approximately 1000.0° C. By way of anotherexample, 1.0 percent by weight of CuO can be added at step 1302 of theformation process to achieve a sintering temperature of approximately1100.0° C. Also, a dielectric ceramic composition having reducedexaggerated grain growth can be achieved. In an example embodiment, adielectric ceramic composition having substantially no exaggerated graingrowth can be achieved. Furthermore, a dielectric ceramic compositionhaving substantially uniform electrical properties and substantiallyuniform density can be advantageously achieved, which can increasemanufacturing yield. By way of example, a dielectric ceramic compositionhaving a dielectric constant of approximately 20.0 can be achieved.

Thus, as described herein, a dielectric ceramic composition having awide sintering temperature range and inhibited exaggerated grain growthcan be advantageously achieved. In contrast, other dielectric ceramiccompositions having Mg, Ca, and Ti typically have a narrow sinteringtemperature range of approximately 5.0° C. to approximately 10.0° C.with significant undesirable exaggerated grain growth. Thus, adielectric ceramic composition having Mg, Ca, and Ti can be formed toyield a wider sintering temperature range and significantly reducedexaggerated grain growth.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

1. A method for fabricating a ferrite disk assembly for aradio-frequency circulator, the method comprising: forming aferrite-based disk that includes a ferrite center portion; and forming ametalized layer on a first surface of the disk to improve electricalcontact between the first surface of the disk with an external contactsurface.
 2. The method of claim 1 further comprising forming a desiredfinish surface on the first surface of the disk prior to the metalizedlayer formation.
 3. The method of claim 2 wherein forming the metalizedlayer includes depositing a film of metal using an ink depositionmethod.
 4. The method of claim 3 wherein forming the metalized layerincludes curing the deposited film of metal.
 5. The method of claim 1wherein forming the ferrite-based disk includes assembling a sinteredrod inside a hollow cylinder, sintering the rod-and-cylinder assembly,and forming one or more disks from the sintered rod-and-cylinderassembly.
 6. The method of claim 5 where the sintered rod is a ferriterod and the hollow cylinder is a dielectric cylinder.
 7. The method ofclaim 1 wherein forming the ferrite-based disk includes securing adielectric ring about the ferrite center portion to define a diskassembly.
 8. The method of claim 7 wherein securing the dielectric ringabout the ferrite center portion includes using a co-firing technique toprovide an adhesive-free joint between the dielectric ring and theferrite center portion, such that the disk assembly can withstandtemperatures in excess of 1000 degrees Celsius.
 9. The method of claim 1wherein forming the metalized layer includes forming a metalized layerhaving a thickness of about one to two skin depths.
 10. The method ofclaim 1 wherein forming the metalized layer includes forming a silverlayer.
 11. A method for improving insertion loss performance of aradio-frequency circulator, the method comprising: forming aferrite-based disk that includes a ferrite center portion; and forming adesired finish for a grounding surface on the disk, the finish selectedto improve an electrical connection between the grounding surface andone or more metal structures, the desired finish having an averagefeature size on the grounding surface that is less than an average sizeresulting from a cut that yields the ferrite-based disk.
 12. The methodof claim 11 wherein the one or more metal structures includes ametalized layer formed on the grounding surface after forming thedesired finish.
 13. The method of claim 12 wherein the metalized layeris a silver layer.
 14. The method of claim 12 wherein forming themetalized layer includes depositing a film of metal using an inkdeposition method.
 15. The method of claim 14 wherein forming themetalized layer includes curing the deposited film of metal.
 16. Themethod of claim 11 wherein forming the ferrite-based disk includesassembling a sintered rod inside a hollow cylinder, sintering therod-and-cylinder assembly, and forming one or more disks from thesintered rod-and-cylinder assembly.
 17. The method of claim 16 where thesintered rod is a ferrite rod and the hollow cylinder is a dielectriccylinder.
 18. The method of claim 11 wherein forming the ferrite-baseddisk includes securing a dielectric ring about the ferrite centerportion to define a disk assembly.
 19. The method of claim 18 whereinsecuring the dielectric ring about the ferrite center portion includesusing a co-firing technique to provide an adhesive-free joint betweenthe dielectric ring and the ferrite center portion, such that the diskassembly can withstand temperatures in excess of 1000 degrees Celsius.20. A method for fabricating a circulator, the method comprising:providing a grounding plane having a first side and a second side;positioning a magnet on the first side of the grounding plane; andpositioning a ferrite-based disk on the second side of the groundingplane, the ferrite-based disk including a metalized layer on a groundingsurface such that the metalized layer is in electrical contact with thesecond side of the grounding plane.